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In-Depth with the 2015 Chevrolet Corvette Z06

February 20, 2014

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What car are we describing? It’s a wedge-shaped, two-seat Chevrolet with a rear transaxle, a front-mounted pushrod 6.2-liter V-8 with an Eaton TVS supercharger nestled in its valley, and some carbon-fiber body pieces. It makes more than 600 horsepower, wears shocks filled with magnetorheological fluid, and is offered with carbon-ceramic brakes nearly as large as those fitted to the Bugatti Veyron 16.4.

If you guessed the dearly departed Corvette ZR1, you are correct. If, however, you guessed the 2015 Corvette Z06, you are also correct. If you guessed anything else, you’re reading the wrong magazine. Because of the upcoming Z06’s striking similarities to the ZR1, we’ve taken to thinking of the new car as the “ZR06.”

Yes, the rip-roaring, high-revving, naturally aspirated, 505-hp 7.0-liter LS7 of the previous Z06 is gone (though it lives on in the upcoming Camaro Z/28). That the new Z06 has a blown engine shouldn’t come as a surprise. We noted about a year ago that the standard Corvette Stingray’s instrument panel includes a digital boost-pressure gauge buried in the driver-information menus. Menus it no doubt shares with the new Z06.

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Note flat-bottomed steering wheel.If it helps you get over the loss of the nasty-wonderful LS7 engine, know that Chevrolet is trying to deliver as much output with the Z06’s new LT4 V-8 as it did with the old ZR1. In other words, a staggering 638 horsepower. But because the Z06 won’t go on sale until early next year, Chevrolet hasn’t settled on a final figure. The company estimates, no doubt conservatively, that the dry-sump LT4 will put out about 625 horsepower. Corvette engineering Grand Pooh-Bah Tadge Juechter says: “It is our aspiration to get to ZR1 power levels. If we can get there, we certainly will.”

He cautions, however, that because the LT4 will use a smaller supercharger than the LS9 engine in the ZR1 (1.7 liters-per-revolution versus 2.3), running about 9.5 psi of boost, it’ll be a stretch. But do not be surprised if it comes very, very close. Know, too, that the company promises the new engine will make at least 625 pound-feet of torque, or 21 more than the former king-of-the-hill Corvette.

That supercharger is mounted atop an engine that uses the standard Corvette’s aluminum block. To handle the increased power, the LT4 uses forged pistons; strong-er, custom-machined steel connecting rods; and titanium intake valves fitted to cylinder heads that are rotocast of A356T6 aluminum for greater strength and heat resistance. It runs a 10.0:1 compression ratio, relatively high for a supercharged engine, thanks in part to the direct-injection system shared with the Stingray’s V-8. The LT4 also uses the same variable-valve-timing and cylinder-deactivation systems as the Stingray’s LT1.

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The Z06’s supercharged V-8 will make at least 625 horsepower.It’s the cylinder-deactivation system, which GM calls Active Fuel Management, along with emissions concerns that prevented the Corvette team from using an updated version of the big-displacement, naturally aspirated LS7. According to Juechter, Active Fuel Management’s collapsing valve lifters cannot reliably handle the high revs that a new version of the LS7 would generate. And if the company had governed revs to spare those parts, the engine wouldn’t make the sort of shock-and-awe power befitting a Z06.

The Z06 will be offered for the first time in the sub-model’s history with an automatic transmission, in this case a new conventional torque-converter unit with eight forward gears. The Hydra-Matic 8L90 is GM’s own design and will reside right next to the standard Stingray’s seven-speed manual on the Z06 order sheet. And yes, before you ask, Chevrolet considered a dual-clutch automatic, similar to the PDK in the

Porsche 911. Juechter claims that the company couldn’t find a dual-clutch that could both fit into the Corvette’s hindquarters and handle the engine’s plentiful torque. Instead, the team sought to match the shift speed of the 911’s PDK, something Chevy claims to have achieved with the paddle-shifted automatic in most circumstances. Either transaxle will be firmly connected to the engine with a Z06-specific carbon-fiber torque tube that’s three times stiffer than the old Z06’s aluminum one.

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Because the Z06 shares its aluminum space frame with the Stingray, the 2015 model will also be the first Z06 to come with a removable roof panel. Chevy figures that this, along with the available automatic, will significantly broaden the appeal of the Z06 over its harder-core predecessors. Considering that automatics outsell manual transmissions by about two-to-one when both are offered in Corvettes, we suspect the company is right about that. The stout structure means that even with its top panel out, the Z06 is some 20 percent stiffer than the old fixed-top car. Predictably, the stiffer structure is also heavier than that of the outgoing car’s. Indeed, it’s one of the reasons that the new Z06 will carry a significantly heavier curb weight. How much heavier? Well, Chevy says it doesn’t really know yet since development is ongoing. But we’re told to expect that it will be weightier not than just the old Z06 (3259 pounds), but also the ZR1 (3353), too. Figure somewhere between 3600 and 3700 pounds and you’re probably close. Still, with the substantial increase in power, the new car should have a pounds-per-horsepower ratio between the ZR1’s 5.3:1 and the old Z06’s 6.5:1.

And Chevy promises that it’s quicker than the old Z06 and faster around the company’s Milford Road Course than either of the earlier hot-rod Corvettes. Both automatic and manual Z06s will have launch-control programs.

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No doubt, the standard Magnetic Selective Ride Control shocks also contribute to the weight increase. The C6 Z06 was only fitted with the magnetic shocks when buyers opted for the Z07 package that also brought pricey carbon-ceramic brake rotors and Michelin Pilot Sport Cup tires. From Juechter’s perspective, making the automatically adjusting magnetic shocks standard means more time to fine-tune a single suspension arrangement instead of both a magnetic and standard one. It also reduces build complexity, something the Bowling Green, Kentucky, plant will appreciate.

The basic suspension pieces are identical to the Stingray’s while the anti-roll bars, dampers, and bushings will be stiffer. How much? Again, Juechter says he doesn’t know yet since development is ongoing and the Corvette team hasn’t yet received the final version of the Pilot Super Sport tires from Michelin. Like the 2013 Z06, the upcoming car will wear 285/30ZR-19s in front and 335/25ZR-20s in the back. Chevy will fit 14.6-inch two-piece brake rotors in front clenched by six-piston fixed calipers, and 14.4-inch two-piece rotors in back with four-piston calipers. Those rotors are bigger than both the standard Stingray’s brakes (12.6 inches in front and 13.3 in back) and those of the 2013 Z06 (14.0 inches front and 13.4 rear).
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And that handling character, according to Juechter, won’t be like the old Z06’s: “The early Z06s—and even to some degree later ones—were a bit of a handful to drive. So that’s the other area of improvement we were looking for. Our goal [with the new car] is an accessible and benign character. It will be very stable and secure.” Another goal is to reduce the new car’s susceptibility to terrain tracking in truck troughs and off-camber roads.

We won’t know how well the team has met its goals until sometime shortly before the car goes on sale in early 2015. The unveiling of the car was pulled forward to January’s Detroit auto show to time it with the premiere of the newest Corvette competition car, the C7.R, which raced at this year’s Rolex 24 at Daytona wearing a facsimile of the Z06’s bodywork. That explains almost everything you need to know about the look of the production car. Maybe we ought to refer to it as the ZR06.R?

You can see in the pictures here that the Z06 has the purposeful look of a track machine. Juechter deems its appearance “brutal.” Surveying all its black aero doodads, vents, and fences, we might go so far as to describe it as gloriously vulgar. Its style is informed by the non-fashion of race cars. It’s the fetishization of function. It is not a pretty thing exactly, but hey, we live in a world where modern Formula 1 cars look like wheeled praying mantises. The model shown here is a Z07 version with the most outrageous of three available aero packages. It has a thick carbon-fiber splitter carrying tall end plates, plus curving carbon-fiber rocker extensions and a tall rear spoiler with a clear center panel that’s height adjustable.2015-chevrolet-corvette-z06-inline1-2-photo-572077-s-original

Left: 2015 Chevrolet Corvette Z06. Right: Corvette C7.R Racer.All of these parts are functional, says Chevy, and deliver the most downforce the company has ever measured for a production car. How much the company is not ready to say. Possibly, you saw that answer coming. The Stage One and Stage Two aero packages will be less outrageous-looking, but all Z06s will have the bigger-than-the-Stingray’s hood vent, the new grille insert, bulging bodywork, the characteristic rear-brake cooling ducts in front of the wheel wells, and those crazy-looking black canopies over the cooling vents in the rear fenders. Said canopies help direct about 50 percent more air, versus the Stingray Z51, into ducts for the transmission and differential coolers (which are also upsized from the Stingray), according to John Bednarchik, the lead aerodynamicist for Corvette. Yes, a NACA duct would have looked even cooler and worked even better there, but there’s no room for one of a sufficient size. Another aero curiosity: Those rocker-panel extensions taper in toward the rear wheel. This is so owners can enter their cars without looking foolish or soiling their pant legs.

Chevy says that owners with the clean pants won’t need to be any wealthier than the guys who bought the old Z06. “If you could afford the old Z06, you’ll be able to afford the new Z06,” says Juechter. The company has not yet set the price on the upcoming car, but Juechter adds that, with every available option, the 2015 model will cost less than $100,000. That’s a lot of money for a Corvette, but it’s still less expensive than the ZR1, with which this car has so much in common.

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